An expected 50 patients with known or suspected inherited myopathy or neuropathy and their families will be recruited for this study. If travel to the Clinical Center is impossible, investigators may come to them to do the tests. Ten to twenty cubic centimeters of blood will be drawn for DNA extraction and genotyping. Some abnormal movements of muscle atrophy will be documented by videotaping. If necessary, diagnostic laboratory and radiographic studies will be done to confirm diagnosis. Because the diseases are hereditary, blood may also be drawn from family members. The family will be counseled and the participants invited back annually to investigate the progression of the disease.